The 75166 Single Aperture Chopper Wheel is a 5 inch (128 mm) diameter wheel with 12 apertures for a 13.7 mm beam. This single aperture model fits in either the 75158 or 75159 chopper head. The wheel is precision etched, and coated with a broadband absorber to minimize retroreflections. You can vary the chopping frequency with the controller. In any situation, the maximum chopping rate depends upon the beam diameter, which determines the maximum number of apertures you can use, and the maximum rotation rate of the motor which is 80 rps for continuous duty operation. The Chopper Wheels Table shows the number of apertures, maximum chopping frequency and beam diameter limit for each wheel, at full modulation. If the beam size is limiting the chop rate, consider focusing the beam at the chopper to reduce the beam size. This allows you to use a wheel with more apertures, and therefore get a higher chop rate.